As for example shown at FIG. 1, a low flow rate cooling system 10 includes coolant piping 12 whereby a liquid coolant flows through a main heat exchanger 14 whereat heat of the coolant is exchanged with the atmosphere, and whereby heat is absorbed from various electronic devices 16a, 16b which may be connected in series, parallel or series-parallel with respect to each other. The coolant flows through a coolant reservoir (or surge tank) 18 having a removable cap 20 whereat filling is performed and air can escape. A pump 22 powered by an electric motor 24 (in combination, simply an electric pump 26) is connected by the coolant piping, the inlet of the pump being connected to the coolant reservoir, and the outlet of the pump being connected to the heat exchanger. The low flow rate cooling system 10 operates independently of the internal combustion engine coolant system 30, the transmission coolant system 40, and the air conditioning system 50. By “low flow rate” is meant that the coolant flows through the piping at a rate much slower than that utilized for internal combustion engine coolant system 30, as for example on the order of about five to twenty liters per minute (5 lpm to 20 lpm).
Motor vehicle applications of low flow rate cooling systems include hybrid motor vehicles and fuel cell motor vehicles. Hybrid motor vehicles utilize electrical components which supplement the internal combustion engine, as for example a power inverter and/or an electric drive motor, and other electrical components. Problematically, these electrical components generate heat which must be dissipated in order to operate within predetermined parameters. As such, a low flow rate coolant system is used to provide the heat dissipation, as needed. Fuel cell motor vehicles may also utilize a low flow rate cooling system for its electronic components, ie., cooling of power inverters, electric drive motors, etc. Also, a low flow rate coolant system may be used with air-to-coolant charge air coolers, as for example either turbo-charged or supercharged powertrains.
While low flow rate coolant systems perform well, there are a number of operational issues that need careful attention. A first issue relates to separation and removal of air bubbles from the coolant after a service fill, which is difficult because of the low coolant flow velocities. Air bubbles removal may require complex steps using vent valves in the system, may take a long time to accomplish, that is, require several system cycles, or may not be possible in some cases. Another issue relates to the fact that low flow rate cooling systems only use electric coolant pumps, wherein the coolant pressure drop at each component must be minimized to keep the size and power consumption of the electric coolant pump as small as possible. Also, the suction side system pressure differential, prior to the electric pump inlet fitting, is critical in achieving maximum pump pressure rise capacity. Yet another issue is that as the motor vehicle is driven, the vehicle motion in the vertical, fore-aft, and side-to-side directions can create churning of the coolant contained within the coolant reservoir of the system. This coolant churning in a flow-through coolant reservoir of a low flow rate cooling system can result in the creation of air bubbles which introduces air into the coolant. Yet another issue of low flow rate cooling systems is that air bubbles in the coolant create a thermal barrier to heat transfer between the electronic component and the coolant and between the coolant and the heat rejecting heat exchanger. Another issue is that multi-path low flow rate cooling systems require a central return path. Yet another issue is that low flow rate coolant pumps can easily loose prime with the introduction of small amounts of air which can render the cooling system inoperative causing thermal stress or failures of the components that are to be cooled by the system.
What remains needed in the art is an air separator for low flow rate coolant systems which facilitates operation of the coolant system and effectively removes air bubbles, while successfully addressing each one of the aforementioned issues.